The recombinant vector vaccine developed by the use of transgenic technology with pathogenic micro-organisms as the vector, can prevent the attenuated vaccine strain getting strong again, but also generate cellular immune responses and has incomparable advantages over traditional vaccines. Currently, research at home and abroad is focusing on genetic recombinant vaccine with a live vector and its mechanism of action. An effective live vector vaccine I is required to have two conditions: first, being safe to host, second, being able to effectively express and deliver the protective antigen having immunocompetence.
At present, research-focused vaccine vectors comprise two categories: one category is attenuated viral vectors, such as the pox virus and adenovirus; the other is enteric pathogenic attenuated bacteria and symbiotic bacteria, such as Salmonella and lactic acid bacteria. Live virus vector can cause effective specific immune response through displaying exogenous antigen on the host cell surface or releasing it into the extracellular environment to make it be recognized by the host immune system. It is possible for the enteric pathogenic attenuated bacteria and symbiotic bacteria after the genetic modification to sustainably and efficiently express autoantigens and exogenous antigens in the host body, thus effectively stimulating protective mucosal immunity, humoral and cellular immune responses against pathogens and foreign antigens. There are inherent weaknesses for the attenuated viruses, enteric pathogenic bacteria and symbiotic bacteria as a live vaccine vector. As a vaccine vector, exogenous genetic fragment that viruses and bacteria can accommodate is small and difficult to carry out large-scale genetic modification. Viral vectors readily trigger host immune tolerance and are difficult to achieve the desired effect by oral administration. Enteric pathogens vectors such as Salmonella easily spread to other parts of the body in the host body, damage other organs and tissues, and cause immune tolerance due to persistent infection; some strains are zoonotic pathogens, which are released into the environment and pose a potential threat to the health of human and animals. In addition, bacterial vectors can not perform glycosylation for the expressed exogenous protein and other modifications, thus causing lack of immune activity of the expressed exogenous protein.
The use of eukaryotes as a carrier will undoubtedly have a greater advantage over viruses and prokaryotes. A larger eukaryotic vector genome can be carried out large-scale genetic modification. And in eukaryotic cells, proteins can be correctly folded and modified to express the target protein with normal activity. Although the challenge use of eukaryotic vectors faces is far greater than viruses and bacteria carriers, because it involves a more complex biological interactions, but since genomic and proteomic research has been relatively mature today, such research can be turned into reality from imagine.
It has been several decades since live oocyst vaccines prepared by blending a variety of attenuated chicken coccidian became available. At present its annual sales have been more than 300 million U.S. dollars, and in the prevention and treatment of coccidiosis in chickens it is playing an increasingly important role. Now study on the interaction between the host and the live oocysts of chicken coccidia vaccine, as well as the immune response mechanism against coccidiosis in the host has been in-depth. However, so far there is no report on application of chicken coccidia as live vector vaccine and application of other Eimeriidae generic coccidia and Cryptosporidium coccidia as live vector vaccine.